Data communication in systems where channel conditions include time varying reflections and/or scattering of the transmitted signal wave is generally more difficult than in systems where a time-invariant signal path exists between the transmitter and the receiver. Fading results when multiple paths from random reflections and/or scattering combine to cancel much of the transmitted signal. Cellular radio systems such as 4G Long-Term Evolution (LTE) and the wireless local area network (WLAN) WiFi (802.11 IEEE Standard) radio system are examples where the fading is largely from reflections. In a forward-scatter radio system the fading results from scattering over small angles, on the order of the antenna beamwidth in the forward direction. A tropospheric-scatter radio link exploits inhomogeneities in the troposphere resulting in forward-scattered signals that can be received at distances beyond the radio horizon. Tropospheric-scatter radio systems may include multiple duplex links for purposes of providing digital data trunks containing digitized voice data and digital data including computer data and Internet traffic. These digital tropospheric-scatter systems are used in commercial applications, for example, for providing communication for oil drilling platforms at sea, and in military applications in both tactical and strategic configurations. Although many digital tropospheric scatter systems were replaced by satellite technology in the 80's and 90's, the utility of rapid deployment of tactical systems and the cost and availability of satellite lease service are factors contributing to the continuing use of digital tropospheric scatter systems.
Prior art techniques have been used to provide adaptive equalization for signal demodulation and compensation for fading with adaptive data rate techniques; however, there is a need in the art for tropospheric-scatter radio systems that provide a transmitter/receiver that employs adaptive data rate fading compensation, covers the large range of delay spread with a large equalization span, considers the use of orthogonal-polarization transmissions, is efficient at low signal-to-noise ratios with higher-order signal constellations, and uses data rate throughput and packet BER as criteria. This need further includes signal demodulation in multiple-transmission applications with acceptable complexity and satisfactory mutual interference cancellation.